The field of the invention is that of assembling machinery, in particular setting a component level in which the ability to view a level is limited.
Spirit levels, in which a bubble of air is trapped within a vial containing a fluid, are well known in the construction and assembly field.
As shown in U.S. Pat. No. 6,449,859, a typical level comprises three vials set at varying angles with respect to an axis of the instrument, typically parallel, perpendicular and at an angle of 45 degrees.
That patent addresses the problem of arranging to view a bubble level that is placed against a nominally vertical surface having an orientation that does not permit the technician using the level to view the bubble in the usual manner.
The bubble that is to be viewed, referred to as the vertical-sensing bubble, is oriented at a right angle with respect to the level axis, so that a viewer looking at the nominally vertical surface will be looking at the bubble end on and will not be able to see the location of the bubble with respect to the reference marks. Normally, the viewer will look at the level along a viewing direction that is parallel to the surface being plumbed.
The situation addressed by this prior art patent is one in which the normal viewing direction is blocked, so that it is not possible to view the bubble in the normal fashion.
The solution provided by that patent is the provision of a mirror oriented at an angle of 45 degrees to the axis of the level and directing the image of the vertical-sensing bubble along an axis perpendicular to the surface being plumbed, so that the vertical-sensing bubble may be viewed from a head on position.
The cited patent provides a reasonable solution to the problem that it addresses, bit is specific to a situation in which there is ample clearance in the vertical direction, so that the entire length of the level, shown as being considerably longer than the height of the technician's head, can fit in the available space.
This reference does not address the problem of a confined and restricted vertical space.
The art would benefit from a level that can be viewed in a vertically restricted space.